The purpose of this project is the development of a non-invasive method of measuring tissue blood flow by analysis of the spectrum of doppler scattered laser light. The prototype instrument has been greatly improved by a new analysis scheme, a four meter flexible fiber optic probe, and the use of a photodiode detection system. The linearity of the instrument in response to blood flow has been greatly improved and noise has been reduced so the instrument can resolve the instantaneous pulsatile flow of microcirculation. The instrument is being used to monitor average blood flow and dynamic blood flow in normal individuals and clinical center patients. Data is being gathered to assess the instrument's usefulness as a measure of blood flow in peripheral vascular disease, carotid artery occlusive disease, sickle cell anemia, and muscular dystrophy.